From Kanye West and Seth Rogen to Alicia Keys and Jessica Simpson, Harley Pasternak has whipped countless celebrities into shape through his famed 5-Factor Diet and fitness plan. After years of traveling the globe with his jet-setting clients, Pasternak has gained insight into the eating and lifestyle habits of the world's healthiest countries and shares his findings in his new book, The 5-Factor World Diet. While focusing on Japan, Singapore, China, Sweden, France, Italy, Spain, South Korea, Greece, and Israel—countries with the lowest obesity and highest life expectancy rates—Pasternak inversely sheds light on why the U.S. is the ninth most overweight country.

What inspired you to write this book?
While obesity has grown in America all we ever do is focus on what we're doing wrong. The problem is we have no perspective. As I traveled the world and saw so many non-overweight people, I thought, instead of focusing on what America's doing wrong, let's focus on what the rest of the world is doing right.

Of the 10 countries you profiled, are there any common themes for staying trim?
With the exception of walking, there's not one specific thing that carries over for all the countries. They all have their own special characteristics and practices. In Japan they practice hara hachi bunme, eating until you are about 70 percent full and waiting 10 minutes to see if you're still hungry. In America we eat until we're full, which means we usually go past the point of satiety because satiety actually follows digestion.

What are some of the best international diet tips you've uncovered?
Choose fish. Japan is the healthiest country in the world, and the Japanese choose fish as their preferred protein source, whereas we definitely overeat meat in the U.S.

Make your plate colorful. A lot of Asian countries make it a point of having five colors present on every dish, which leads to eating nutrient-rich foods.

Watch the fruits you eat. All the healthiest countries don't eat a lot of tropical fruits. They stay away from pineapples, mangos, papayas, and melons and focus on fruits that have edible skin, edible seeds, or are citrus fruits. Fiber is found in the skin and seeds of fruit and citrus fruits are high in acid, so they don't make your blood sugar surge.

Don't be scared of dairy. The Swedes are one of the healthiest people and they put a high value on dairy. It's one of the best quality proteins you can put in your body and has vitamin C, calcium, vitamin D. Just know there are low-fat dairy options. In Sweden they also make open-face sandwiches with one piece of bread, which is half of what Americans use.

From mezze in Greece to dimsum in China, there's also the idea of eating multiple small dishes rather than having one great big one. Portion control is really important—in France, they don't necessarily eat what I'd consider the healthiest foods but they eat small portions and really savor the flavors. Also, half of the healthiest countries in the world eat with chopsticks: When you eat with chopsticks, you can't generally eat as much or as quickly as you might otherwise.

You write about how the French get on their bikes every day to buy what they're going to eat instead of stocking up for weeks like Americans do. What other healthy lifestyle tips did you find?
One thing is to not look at fitness as something that you do at a prescribed time of day in a prescribed room and a prescribed building. You should incorporate physical activity throughout your day. Studies have shown that any culture that uses public transportation is actually healthier and less overweight because it requires that you walk up stairs or walk to the subway or bus.

The Italians also do something called passeggiata, which is a tradition of getting up after a meal and walking with their family around the neighborhood. That's just something we don't really consider in the U.S.

And in Greece they put a lot of value on sleep and afternoon naps. In general, a lot of places in southern Europe understand that people who are sleep-deprived have higher stress levels and can consume more food as a result. Also, the more hours of the day that you're awake, the more you're going to eat. In America we place less emphasis on sleep than anywhere in the world.